1. Field of the Invention
The invention in general relates to temperature sensing apparatus, and particularly to such apparatus utilizing acoustics.
2. Description of the Prior Art
In the operation of industrial apparatus, it is often desired to know the temperature at various locations within the apparatus itself. One simple method of accomplishing this temperature sensing is by the use of thermistors which may be placed at various desired locations. The themistors provide respective output signals indicative of the localized temperature and these signals are conducted by means of wires to a central location for utilization of the information.
For some types of apparatus, for example, high voltage power transformers, the utilization of thermistors with wires leading to the transformer tank wall would be highly undesirable.
To eliminate the requirement for low voltage signal carrying wires extending to the transformer tank wall, proposals have been made for temperature sensors which incorporate a radio transmission unit. The sensor includes a frequency determining element which varies in accordance with the temperature and receiver apparatus at the tank wall, receives the transmitted signal, which is an indication of the temperature in the vicinity of the sensor. Various points in the transformer may be monitored by utilization of various sensors operating at respectively different frequencies.
The costs of these radio transmission sensors can be extremely high due to the required ultrahigh reliability and for many transformers the maintenance required for proper operation of these radio transmitting sensors is not justified.
The present invention provides a sensing system particularly useful for high voltage transformers and in which the sensing apparatus within the transformer tank is passive, and without the requirement of any metallic connection to the transformer tank wall.